Jeff knows that adding a special grain supplement to his cows will produce more milk according to the following schedule: 

1/4 2/7 3/10 4/12 5/13 6/14

where the first number reports the total number of pounds of grain supplement, and the second number reports the total amount of milk produced. For example, 4/12 means that if the cow is fed 4 pounds of grain supplement, the cow will produce 12 units of milk. 

How many pounds of grain supplement should Jeff feed the cows if the farm receives $0.30 per unit of milk and the price of grain supplement is $0.80 per pound?